PALAEONTOLOGY OF NEW-YORK. 
Fig. 5 & 6. Interior of a small and a large ventral valve. 
Fig. 7. The ventral valve enlarged. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Helderberg mountains; Catskill, Hudson, Schoharie, and other places. 
Leptocoelia imbricata. 
Plate XXXYIII. Fig. 8 - 13. 
Shell longitudinally semielliptical or suborbicular. Ventral valve convex, 
most prominent along the middle, and sloping laterally : beak small, 
incurved at the apex and perforated by a very small round aperture, 
one side of which is formed by the deltidium. Dorsal valve flattened 
or depressed convex : beak scarcely elevated above the hinge; hinge 
line sloping from the beaks at an angle of about 150°, rounded at the 
extremities, nearly equal to the greatest width of the shell; false area 
narrow, much shorter than the hinge. 
Surface marked by ten to twelve plications on each valve, of which two 
on the middle of the ventral valve are larger and more elevated than 
the others, and separated by a wider and deeper depression than be¬ 
tween those on each side. The central plication on the dorsal valve 
is larger than the others near the front, but usually dies out before 
reaching the beak. Shell marked by strong imbricating concentric 
lamellee of growth. 
This species resembles Leptoccelia (Jltrypa) disparilis of the Niagara group, but 
is generally larger, has more plications and a straighter hinge : its dorsal valve also 
differs, in being slightly convex instead of concave. It also bears a general resem¬ 
blance to Terebratula lepida (Goldfuss) and T. sublepida (de Verneuil), but has a 
wider hinge than either of these, and differs likewise from them in other obvious 
and essential characters. 
Fig. 8, 9 & 10. Illustrations of the dorsal and ventral valves of the ordinary forms of this • 
species. 
Fig. 11 & 12. Individuals differing somewhat in the plications from the more common forms. 
Fig. 13. Dorsal view of a specimen enlarged. 
The comparative extension of the hinge line in different individuals is subject 
to much variation. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Helderberg mountains; Schoharie, and other places. 
